The port circuit breaker is a small outdoor landing tank structure, equipped with CT14 spring operating mechanism; The mechanism and the body are installed together, which is simple to install, convenient to debug, reliable and suitable for frequent operation. The service life of the mechanism is more than 3000 times; The mouth adopts the pressurized air arc extinguishing structure, which has a strong breaking capacity. The total breaking capacity of 40KA is up to 12 times, which is the highest in China. Reliable sealing performance. Imported sealant gasket is adopted, the dynamic seal is made of "V" type sealing ring with spring pressure compensation structure, and the secondary junction board of mutual inductor is provided by the joint venture to ensure the annual air leakage rate & LT;0 5%;The internal current transformer is made of microcrystalline alloy with high magnetic conductivity. The exact level can reach 0.2 or 0.s. According to the needs of users, 12 transformers can be attached. No reignition for 50 km of the no-load line.